Electrical switching apparatus



July 28, 1959 M, PjR ECE 2,897,322

ELECTRICAL SWITCHING APPARATUS Filed April 16, 1957 2 Sheets-Sheet 1 Inventor A Home y July 28, 1959 M. REECE ELECTRICAL SWITCHING APPARATUS 2 Sheets-Sheet 2 Filed April 16, 1957 Inventor M W M Attorney United States Patent ELECTRICAL SWITCHING APPARATUS Michael Peter Reece, Greenford, England, assignor to E.R.A. Patents Limited, Leatherhead, England, a British company Application April -16, 1957, Serial No. 653,090 Claims priority, application Great Britain April 24, 1956 7 Claims. (Cl. 200-146) This invention relates to circuit breakers for alternating current where the electrodes are mounted in a highly evacuated envelope.

In such circuit breakers, separation of the electrodes leads to the formation between their contact surfaces of a small number of bridges of molten electrode metal which explode as the separation proceeds and leave corresponding arcs.

When the separation starts just after a current zero, the bridges are quite small and their explosion therefore does little damage to the contact surfaces. The cathode spots of the arcs which are left by these bridges are found to multiply quickly and spread out more or less uniformly over the contact surfaces so that arcs become distributed over these surfaces. These surfaces are always made sufficiently large to ensure that the current density at them when the following current maximum is reached is insufficient to cause general overheating of the surfaces.

It the separation of the electrodes is started at a later epoch of the current cycle up to the current maximum, the bridges formed become larger in size, and greater damage is therefore done to the contact surfaces when these bridges explode. The corresponding arcs left after this explosion of course then have to carry larger instantaneous currents, and the cathode spots of these arcs, instead of spreading out over the contact surfaces, remain concentrated on the molten patches which were left on the contact surfaces at the places formerly occupied by the bridges. There is some evidence to show that this con centration of cathode spots takes place when the instantaneous current is greater than a somewhat ill-defined value (which is of the order of 10,000 amperes for copper electrodes). This concentration of the cathode spots and thus of thearcs, which it will be noted takes place no matter how large the contact surfaces are made, keeps the temperature of the molten patches high so that these remain overheated. Such overheating leads, in the case of copper electrodes, to these patches remaining in the molten state, with consequent increased damage, while in the case of all the metals commonly employed in manufacturing electrodes (i.e. copper, steel and tungsten) the resultant high vapor pressure exerted by the electrode metal in the gap between contact surfaces often causes re-ignition of the arcs after the next current zero when the re-striking voltage is applied.

According to the present invention, three or more pairs of cooperating electrodes are provided, including a main pair and two or more auxiliary pairs which are of lower arcing voltage than the main pair and which are each connected electrically in parallel with the main pair, and the operating mechanism of the circuit breaker is designed so that during the breaking operation it first separates only the cooperating electrodes of the auxiliary pairs, so that in operation to interrupt a current, bridges of electrode metal first form and then explode between cooperating electrodes, and then the mechanism separates the electrodes of the main pair, the arrangement of the electrodes ice being such that an are at the main pair or an arc at any one of the auxiliary pairs can cause the formation of arcs at all the auxiliary pairs. The pair of electrodes of higher arcing voltage are referred to as the main pair merely for convenience rather than to indicate their size or conductive capacity relative to the auxiliary pairs. Again for convenience the electrodes of the main pair, their contact surfaces and any are formed between them are referred to as main electrodes, main contact surfaces and a main are respectively, whilst the word auxiliary is employed for corresponding terms referring to the auxiliary pairs.

In a circuit breaker constructed according to this invention, the bridges formed between cooperating auxiliary contact surfaces are smaller than corresponding bridges found in known circuit breakers which have but one pair of electrodes, and the auxiliary arcs have a smaller current than corresponding arcs found in such circuit breakers. There are two reasons for this. First of all, some of the current is diverted through the main electrodes, which are of course still in contact. It will be realized that an immediate and complete diversion is not possible owing to the finite inductance of the auxiliary pairs. The second reason is that the current which is not diverted divides between the different auxiliary pairs. This division of current is surprising and investigation has shown that this division is due to the previously unknown fact that the voltage-current relationship for arcs in a vacuum is positive so that an increase in the current passing through an arc leads to an increase in the voltage across it. It is well known that arcs in air have, on the contrary, a negative voltage-current relationship and that if, therefore, an air-break type of circuit breaker were provided with more than one pair of cooperating electrodes, an arc would be maintained at only one of them on their separation.

Thus in a breaker according to the invention the bridges are smaller than in known breakers having one pair of electrodes and dealing with the same current, and the damage to the contact surfaces is correspondingly smaller. At the same time, the currents which can be handled without concentration of arcs and consequent overheating taking place is larger.

When the bridges between cooperating auxiliary contact surfaces have exploded, the main electrodes are separated. The main arc then formed does, of course, cause a certain amount of damage at the main contact surfaces, but this does not matter owing to the continued good condition of the auxiliary contact surfaces. This main arc very quickly dies out because any auxiliary arc in existence grows at its expense owing to the diflerent arcing voltages of the main and auxiliary pairs, while if the auxiliary arcs have themselves died out before the main electrodes are separated, such arcs are started again by the arc-initiating energy (which may be metal vapor or electrons or radiation) which is emitted from the cathode spots of the main arc and which is travelling towards an auxiliary contact surface (on arriving, this energy initiates cathode spots). It will be realized that if the main electrodes were separated before the bridges between cooperating auxiliary contact surfaces exploded, and if this separation took place at a moment when a large instantaneous current was flowing through the breaker, the diversion of current back again from the main pair to the auxiliary pairs would lead to an increase in the size of the bridges, with consequent increased damage on their subsequent explosion.

In the final stage of the current interrupting operation,

the auxiliary arcs themselves are extinguished at a current zero.

When the current interrupting operation is started near ate the breaker.

397,322 I V v r .a current rzero, it sometimes happensthat only one aux .iliaryarc forms v(this .may be the result of slight difierences in the construction of the auxiliary electrodes) so that if no other auxiliary arc were started the current at '-I .a Xi Y'P con erne uul rbe serera *times :greater than usual, with tconsequent increased damage. In a breakeraecording to the -.inyention{ ;other auxiliary arcs ;are started due to the airangement of .the

auxiliary electrodes, which is suchthateyvhen an larc' iis :formed-at anyone of the auxiliarypairs, the arc-initiating -.energy emitted passes towards at least; one of the other -=.auxiliary pairs ,andstarts thereanvarc, which ,then emits energy to start a further arc,;and so on -until there are ,arcs atall the auxiliary pairs. g

'In .a preferred rformvof construction, shiel'ds -whi ch remain relatively cool during current interrupting oper- -,.ations of the breakerarc arr n ed and: shaped so .as to intercept and adsorb a major proportion, of v all arcinitiating energy emitted-onarcing, which, isnot travelling ztowards a contact surface of any .aux iliary electrode. Thisadsorption greduces the amount of-ener-gy travelling :intoregions of the envelopepther thanthosein the neighbourhoodpof the contact, surfaces, and thus-reducw the .-;risk of re-ignition after a current zero over- ,long paths in the first-mentioned regions.

in order that the invention may-be,rmoreeasily -understood and readily carried intoeficct, a ecirc uit breaker constructed according to, it andcapable of handling 15,Q( ,.-R.M.S. amperes, together with a modified form of construction, will now be described with referencetothe accompanying drawings in which:

Figure 1 is an elevation, partly insection, of the-,cirgcuit breaker;

Figure 2 is a cross-section taken along the line I I, H of Figure 1;

vFigure 3 is an;elevation similartoEigure l butshowing'the modifiedflformof construction; and

Figure 4 is a cro,ss section similar to Figure 2 but taken along thegline IV.IV of Figure 3.

Referring first of all to Figures 1 and 2, the circuit :breaker includes two main, vertically disposed cooperrating electrodes laand 1b, made oftungsten and of; one .inch diameter, and fourteen auxiliary, vertically-disposed copperelectrodes of half inch diameter and withhemi- .spherical ends, the eight upper, ones being; indicated at 2a and the six lower "ones at,2b. ,As is bestseen in Figure 2, the electrodes 2a and 2b are arranged symmetri- ,cally in a ring around the main electrodes 1a and 1b, ;and :the arrangement is such that, the rings ;of upper and lower electrodes .2a and- 2b interfitywithone anotherso -that each of the six lower electrodes lb engages its -.two eznearestneighbours. ;By this arrangement,-the fourteen .electrodes cooperate with each other 1at=twelve placesand so produce twelve auxiliary pairs.

;The main electrode 1'!) is mounted on acoppenstem :3 to which one of the conductors :for;alternati g;current, ,indicated at 4, is securedflby nuts-:5. IThe ste m .3;is 9Qnnected throughan insulating sleeve 16. to :a mechanism (not shown) for moving :the stem 3111p and;dowjn,to oper- This stem .3. not-only carries ,the main electrode 1b but also aconducting:disciSZQnM/hich ,all

the electrodes 2b are mounted, .beingsecured in position -bynuts9.

The upper auxiliarye'lectrodesla are-ia'll screwed into a fixed conductingihanger so that these electrodes 2a are immovable. The upper mainelectrode'la is, ,on the other hand, secured to a' copper .stenrlfi which ,is ver- :,.tically movable. This stem 16 passes upwards through an opening in the hanger 1'5 and .an opening in a iconducting disc .17 secured tozthe :hangerlil'i andatjts top end the stem 16 carries nuts 18 holdingin position the ,other conductor for alternatingcurrentindicated at 19. spring 20 presses downwardly on;th e se nuts 18 ;to keep the main electrodes 1a and 1b in engagernent. conti 1 r 11 t t lti sa ai aav u 17 so that each auxiliary pair of electrodes 2a and 2b are velectri callyin parallel with main pa ir laand 1b.

When the sleeve 6 is moved downwardly from the position shown in Figure :1, the auxiliary electrodes 2a and 2b separate and, in general, bridges form and explode between the electrodes of each auxiliary pair and auxiliary arcs then form. The main electrodes 1a and 1b, however, do not separate during this initial stage of the breaking operation, since the upperinain "electrode 1a is :moved downwardly by the spring-Mend kee ps in engagement with the electrode 1b. During this downward movement of the electrode 1a a collar 30 secured to the stem 16 engages a fixedstopfil so thatthe electrode 1a comes to an abrupt halt when the contact surfaces of the electrodes of each auxiliarypair are separated by about '5 Separation.of the main e ectrodes 1a and 112 then follows, with the formation of g the main arc.

"The formation and extinction of the main and auxiliary arcs have already be'en described in detail andneed only be referred to briefly here. The auxiliaryarcs,

formed during the initial stage of the current interrupting operation, havea low current fo'r'reasons already mentioned sothat major damageiof the auxiliary electrodes 2a and 2b is avoided. When the main are forms atthe tungsten electrodes 1a and 1b on their separation, this faces -of all the electrodes are arranged at about-the same level, so that arc initiating ener'gy er'nittecbby the mam arc is able to reach the auxiliary contact surfaces so astostart auxiliary arcs, if--these do notvalready exist.

-It should be noted that the lower auxiliary contacts 2b remain fixed with main contact-lb ata1l times and the upper ends of the auxiliary contacts 2b interseotth'e-common plane of the contacting faces of the main contacts 1a and 1b, so that when-the main contacts open, arcfmrtlatrng energy travels' outwardly in common plane and strikes the contact surfaces of auxiliarylcontacts 2b.

'By properlyv selecting the'jarnount gor overlap" between auxiliary contacts 2a and 2b, and by properlypds'itidnihg the collar 30 with respect to the fixed stopl31,]the lower endsof the upper'aux'iliarycontacts 2b mayl-alsointersect I the common surface-contacting plane of thejm'ain 'elo trodes at the time of opening ofthe main electrodes. This arrangementofthe contact surfaces also ensuresthat o -energy from an are at anyauxiliary pairisable' to reach 5 start arcs there, if these-do not already exist.

the auxiliary contact surfacesof other auxiliary pairs to Two shields in the form of inner nd ue; coaxial cylinders 35 and 36 are arranged so' thatthe-inner'cyllllldfil 35 surroundsonly the pair Ia and l bf whilst theouter cylinder 36 surroinids all thepairs. In area to permit the formation of am at all theauxiliarfilpairs -iby an arc at the inain pair, th e inne r cylinderi'is formed with a large-number of openings :38; the

.be clear-that passage or energy from anyjuxilialryielecpassagepof energy -froni the arc-at the main ,pair contact surfaces of each 'of the auxiliary pairs. It

. trode to adjacent ones is ndtinter fered the operations. of the circuit breaker 'isato,intercept and cylinders 35 and 36. p .s

The function of these cyliriders 3 5 and 36, which remain cool relatively to the regions of arcing during adsorb energy whichisw emitted-ion arcing and which is not travelling towards- ,a contact .su rfacelof an electrode. -fIhisadsorptibnof energyprevents its escape from the .regionsiintthe neighboiirhoodrof.theicontact surfaces, andthus. i-reduces. .the risk, or r-rerignition ,over

long. Paths win the .envelopel aftera .cuifrentizero. 5 The cylinders are, anneal-amide .tothe. eleetrodes. as", is

wrest-b reenest-on ae aaseeseeea of the breaker, and they also extend a substantial distance along each electrode.

The inner sleeve 35 is held in position within the outer sleeve 36 by metal spacing bars 40, while the outer cylinder 36 is held in position in the envelope of the circuit breaker by further metal bars 41. The envelope itself consists of a metal cylinder 42, to which the bars 41 are brazed, a glass cylinder 43 secured to the upper end of the cylinder 42, a metal end fitting 44 secured to the cylinder 43 and brazed onto the hanger 15, a further glass cylinder 45 secured to the lower end of the cylinder 42, a further metal cylinder 46 secured to the cylinder 45, an end fitting 48 and a box-like structure 49 similar to the hanger 15 and annulus 17. Metal bellows 50 and 51 are provided within the hanger 15 and the structure 49 respectively to complete the envelope, and to allow the movements of the various electrodes to take place. A tube 52 is provided in the structure 49 to enable the envelope to be exhausted, this tube 52 being sealed ofl: after rigorous de-gassing of the envelope and its contents, and when the pressure is of the order of to 10* mm. of mercury.

In the form of construction shown in Figures 3 and 4, only ten auxiliary electrodes are provided and these are arranged, in completely separate pairs, in a ring around the main electrodes. Each of these pairs of auxiliary electrodes is surrounded by separate cylinders 55 which are held in position by metal bars 56 secured to the metal cylinder 42. These cylinders 55 perform the same functions as the cylinders 35 and 36 shown in Figures 1 and 2, and in order to permit the passage of energy to all the auxiliary pairs, these cylinders are formed with openings indicated at 57.

In a modification (not shown) of the form of construction shown in Figures 1 and 2, each auxiliary electrode engages its two nearest neighbours after a making operation.

I claim:

1. A circuit breaker for alternating current comprising a highly evacuated envelope, a main pair of cooperating metallic electrodes mounted in said envelope, at least two auxiliary pairs of cooperating metallic electrodes mounted in said envelope in laterally spaced relation with respect to each other and with respect to said main electrodes, said auxiliary electrodes being formed of a metal of lower arcing voltage than said main electrodes and each of said auxiliary pairs being connected electrically in parallel with said main pair, and means for operating said breaker, said means acting during the breaking operation first to separate only the cooperating electrodes of the said auxiliary pairs, whereby in operation to interrupt a current, bridges of electrode metal form and then explode between said cooperating electrodes of said auxiliary pairs, and said means then acting to separate the electrodes of said main pair, the electrodes of the said main and said auxiliary pairs being such that an are at the said main pair causes the formation of arcs at all the auxiliary pairs and such that an are at any one of the auxiliary pairs causes the formation of arcs at all the auxiliary pairs the engaging surfaces of the main electrodes as they are about to sep arate, being in a common plane passing through a contact surface of at least one electrode of each of said auxiliary pairs of electrodes, whereby an arc at the main pair produces arc-initiating energy which travels in said plane and causes formation of arcs at all said auxiliary pairs.

2. A circuit breaker according to claim 1, and also comprising shielding means about the auxiliary electrodes which remain relatively cool during current interrupting operations of the breaker, said shielding means being mounted in said envelope and constituting means for intercepting and adsorbing a major proportion of all arc-initiating energy, emitted on arcing, which is not travelling towards a contact surface of any of the said auxiliary pairs, and openings in the shielding means to permit flow of arc-initiating energy between the main and auxiliary electrodes.

3. A circuit breaker according to claim 2, said shielding means comprising two substantially coaxial cylinders, said main pair being arranged within the inner cylinder, and the said auxiliary pairs being arranged between the said cylinders.

4. A circuit breaker according to claim 1, said auxiliary pairs comprising at least six electrodes, of which the electrodes connected electrically to one electrode of said main pair are fixed in position in said envelope and are arranged symmetrically around the said one electrode to constitute a first ring of electrodes whilst the electrodes connected electrically to the other electrode of said main pair are secured together and movable as a unit in said envelope, and are arranged symmetrically around the said other electrode to constitute a second ring of electrodes.

5. A circuit breaker according to claim 4, said rings of electrodes being arranged to interfit with one another when brought together, whereby electrodes of the said auxiliary pairs then engage their two nearest neighbours.

6. A circuit breaker according to claim 1 in which said main electrodes are formed of tungsten and said auxiliary electrodes are formed of copper.

7. A circuit breaker according to claim 1 wherein more than two pairs of auxiliary electrodes are mounted within said envelope and are arranged in a circular array about the common axis of said main electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,821,414 Allan Sept. 1, 1931 1,875,765 Scherbius Sept. 6, 1932 1,996,304 Millikan et a1. Apr. 2, 1935 2,180,661 Baruch Nov. 21, 1939 2,794,885 Jennings June 4, 1957 FOREIGN PATENTS 400,716 Great Britain Nov. 2, 1933 

